A great number of electronic ballast circuits for igniting HID lamps are known and utilized. All known half-bridge ballasts suffer from the drawback of their failure to protect the ballast against damage during the starting or striking period of the lamp when the lamp is out of order and will not ignite.
For the sake of completeness and better understanding, a typical prior art HPS ballast circuit such as those referred to above, is shown in FIG. 1. The circuit is illustrated and described in detail in an article by Peter N. Wood, entitled "Electronic Ballasts Using the Cost-Saving IR2155 Driver," MOS-Gate Driver Data Book, E50161, International Rectifier Application Notes (1995).